1. Field of the Invention
The Present invention relates to a polymer foam comprising styrene acrylonitrile copolymer and one or more infrared attenuating agent such as carbon black and graphite. The invention further relates to a process for preparing such a foam.
2. Description of Related Art
Chlorinated blowing agents, particularly chlorofluorocarbon (CFC) and hydrochloroflubrocarbon (HCFC) blowing agents, have historically served two important roles in insulating polymer foam technology: as blowing agents and as thermal insulating components in polymer foam. However, concerns over how CFC and HCFC blowing agents affect the environment have led to regulations on their use. These regulations have motivated innovation of alternative means for enhancing the thermal insulating capability of polymer foam while using blowing agents other than chlorinated blowing agents.
Inclusion of infrared attenuating agents (IAA) into polymer foam has been one approach to enhance the thermal insulating capability of polymer foam apart from chlorinated blowing agents. IAAs can enhance thermal insulating capability by absorbing, reflecting or absorbing and reflecting infrared radiation. An IAA inhibits penetration of infrared radiation through a foam containing the IAA. There are, for example, numerous references disclosing examples of polystyrene foams containing carbon black and graphite as IAAs.
U.S. Pat. No. 4,795,763 ('763) teaches that carbon black is useful for incorporating into rigid foamed plastic materials to enhance thermal insulative properties of the foamed plastic material. '763 provides specific examples of polyisocyanurate foams and teaches that in the broadest aspects of the invention the plastic materials are polyurethane, polyisocyanurate, polyurea, polyolefin, polystyrene, phenol-formaldehyde, epoxy and other polymeric foams.
European patent (EP) 0372343 ('343) teaches that inclusion of carbon black into close celled foams of styrene polymers and copolymers can reduce the thermal conductivity of those foams. '343 provides specific examples of polystyrene foams containing carbon black.
Published patent application WO 94/13721 discloses a particularly beneficial form of carbon black for dispersing into polymeric foam and provides specific examples of polystyrene foams containing the carbon black.
EP 1196486 and EP 1031600 disclose styrene based polymer foams containing graphite particles. EP1661939 discloses styrene based polymer foams that can contain IAAs such as carbon black and graphite.
While these references disclose benefits of reducing thermal conductivity when incorporating carbon black or graphite into polymer foam, none of them address the effect of an IAA on dimensional integrity of a foam, particularly at elevated temperatures. Having a high dimensional integrity at elevated temperatures is important to ensure that an insulating foam will not change dimensions to any significant extent when used in high temperature insulating applications.